This invention relates generally to a vapor deposition apparatus and more particularly to a vapor deposition apparatus having a deposition enclosure accessible from within a cleanroom.
Coating materials are often used as protective barriers on circuit boards, integrated circuit devices, medical devices and the like to protect the devices from moisture, contaminants, corrosives and chemicals. One exemplary coating material is parylene, which is the generic term for the inert nonconductive polymers in the family of unsubstituted and substituted poly-p-xylylene. Parylene has three primary variations typically referred to as parylene C, parylene N and parylene D. Each of these three variations may be deposited on an item as the chemical is converted under vacuum and heat from a powdered dimer form to a clear polymer film. Unlike liquid coatings, parylene is deposited in equal thickness on all surfaces, including around sharp edges and in deep crevices of the item being coated. Reference may be made to U.S. Pat. No. 4,163,828, incorporated by reference herein for all purposes, for additional information regarding the chemical composition of parylene coatings and the parylene deposition process.
Parylene is applied to an item to be coated at room temperature with deposition equipment that controls both the coating rate and the coating thickness. Parylene deposition takes place at the molecular level as a powdered chemical is vaporized under vacuum and heat to form a dimeric gas. The dimeric gas is pyrolized to cleave the dimer to its monomeric form. The monomer gas enters a room temperature deposition chamber where it simultaneously adsorbs and polymerizes on the item. Typical parylene deposition equipment includes a vaporizer where the dimer is vaporized by heating, a pyrolysis furnace where the dimeric gas is pyrolized by further heating, a deposition enclosure where the coating is deposited on the item to be coated, a cold trap to filter excess parylene passing through the deposition chamber, and a vacuum pump downstream of the cold trap that creates vacuum pressure throughout the system. Reference may be made to U.S. Pat. Nos. 4,163,828, 5,264,039 and 5,908,506, incorporated by reference herein for all purposes, for additional background information regarding parylene deposition equipment.
Medical devices, integrated circuit devices, and other devices that are frequently coated with parylene may be manufactured, or otherwise processed, in a cleanroom to prevent contamination of the devices by dust, chemical substances in the air, or other impurities. Preventing contamination of these devices improves the performance characteristics of the final products utilizing these devices and eliminates failures associated with such contamination. Cleanrooms are rooms in which the concentration of airborne particles is controlled to specified limits. Cleanrooms typically use high flow capacity ventilation systems with high efficiency filters that frequently recycle the total volume of air within the cleanroom to maintain the desired level of concentration of airborne particles. Cleanrooms are expensive to operate and difficult to maintain substantially free of airborne contaminates. Reference may be made to U.S. Pat. No. 6,368,208, incorporated by reference herein for all purposes, for additional information regarding cleanrooms and cleanroom ventilation.
Existing high volume vapor deposition machines are not well suited for operation in a cleanroom environment. Contaminates in the form of the solid parylene dimer or other airborne contaminants are generated by operation and maintenance of such machines. These contaminates contribute to contamination of the cleanroom and prohibit effective operation of such machines in a cleanroom. Further, during normal operation of the vapor deposition machine, the deposition chamber and the cold trap must be periodically cleaned to remove excess parylene that builds up on the internal surfaces of these items. This routine cleaning cannot be done in the cleanroom without contaminating the air quality in the cleanroom. Further, portable deposition machines that can be operated from within the cleanroom and removed from the cleanroom for cleaning have a reduced capacity which limits their use to small scale production runs, thus increasing the cost of the items being manufactured. Also, a portable deposition machine is not ideal for operating in a cleanroom because airborne contaminants generated when solid coating material is loaded into the machine may degrade the air quality in the cleanroom. Therefore, there is a need for a vapor deposition machine that allows coating of an item manufactured or otherwise processed in a cleanroom without jeopardizing the air quality of the cleanroom.